1. Field of the Invention
The present invention relates to an image recording medium including an electric accumulator that accumulates electric charges in a quantity corresponding to an electromagnetic wave irradiated for recording as electric charges for a latent image. The present invention also relates to an image retrieving method and an image retrieving apparatus to retrieve an electrostatic latent image recorded on the image recording medium.
2. Description of the Related Art
A conventionally-known method for use in medical radiography or the like is a method utilizing, for example, a radiation image recording medium (an electrostatic recorder) as a photoreceptor. The radiation image recording medium, which includes a photoconductor such as a selenium plate sensitive to radiations such as X-rays, is used as an image recording medium having an electric accumulator for accumulating electric charges in a quantity corresponding to irradiated electromagnetic waves for recording as electric charges for a latent image. In the foregoing method, X-rays are irradiated onto the radiation image recording medium to allow the electric charges in a quantity corresponding to the irradiated radiation to be accumulated in the electric accumulator inside the radiation image recording medium, whereby radiation image information is recorded as an electrostatic latent image. Moreover, the radiation image information is retrieved out of the radiation image recording medium by scanning the radiation image recording medium, on which the radiation image information is recorded, with a laser beam or a line light source (as disclosed in U.S. Pat. No. 4,535,468, for example). It is possible to attempt reduction of radiation dosage of a test subject and enhancement in diagnostic performance by use of the radiation image recording medium.
In Japanese Unexamined Patent Publication No. 2000-105297 and in Japanese Patent Application No. 10 (1998)-271374, there has already been disclosed a radiation image recording medium which is capable of combining high-speed response upon reading out and efficient extraction of signal charges, a recording apparatus for recording radiation image information on this radiation image recording medium, and an image retrieving method and an image retrieving apparatus for retrieving the radiation image information out of the radiation image recording medium, on which the radiation image information is recorded as the electrostatic latent image.
The method disclosed in Japanese Unexamined Patent Publication No. 2000-105297 includes the steps of using a radiation image recording medium including a first electrode layer which transmits radiation for recording or light emitted by excitation of the radiation, a recording photoconductive layer which takes on conductivity by receiving irradiation of the radiation for recording or the light, a charge transport layer which acts substantially as an insulator with respect to electric charges for a latent image and acts substantially as a conductor with respect to transported electric charges having a reverse polarity to the electric charges for a latent image, a retrieving photoconductive layer which takes on conductivity by receiving irradiation of an electromagnetic wave for retrieval, and a second electrode layer which transmits the electromagnetic wave for retrieval, the radiation image recording medium in which the foregoing constituents are stacked in accordance with the above order of enumeration, irradiating the radiation for recording onto the first electrode layer of the radiation image recording medium, recording radiation image information as an electrostatic latent image by allowing electric charges in a quantity corresponding to the dosage of the irradiated radiation to be accumulated in an electric accumulator formed substantially at an interface between the recording photoconductive layer and the charge transport layer, and obtaining the radiation image information by reading the recorded electrostatic latent image by irradiation of the electromagnetic wave for retrieval.
In addition, there has also been disclosed a radiation image recording medium, in which the second electrode layer is a stripe electrode composed of multiple line electrodes arranged in a stripe configuration which transmit the electromagnetic wave for retrieval. The foregoing radiation image recording medium can accumulate the electric charges for a latent image intensively in the electric accumulators corresponding to the respective line electrodes of the stripe electrode. Accordingly, it is possible to enhance sharpness of an image.
In the foregoing radiation image recording medium, if a direct-current voltage is applied such that the first electrode layer is charged as negative electric potential and the second electrode layer is charged as positive electric potential, and if the radiation which passed through an imaging object is irradiated onto the first electrode layer of the above-described radiation image recording medium, then charge pairs are generated on the recording photoconductive layer as corresponding to the dosage of the radiation owing to irradiation of the radiation that passed through the first electrode layer. Accordingly, negative electric charges are accumulated in the electric accumulator as the electric charges for a latent image, and the radiation image is recorded as the electrostatic latent image.
Moreover, if application of the direct-current voltage is discontinued and re-arrangement of electric charges are performed by short-circuiting the first electrode layer and the second electrode layer, and if the electromagnetic wave for retrieval is subsequently irradiated onto the second electrode layer of the radiation image recording medium, then the electromagnetic wave is transmitted through the second electrode layer and irradiated onto a retrieving photoconductive layer, whereby charge pairs are generated in the retrieving photoconductive layer. Among those charge pairs, positive electric charges are transmitted through the charge transport layer and coupled with negative electric charges accumulated in the electric accumulator. Meanwhile, negative electric charges cause electric discharge owing to re-coupling with positive electric charges that are charged on the second electrode layer. Retrieval of the electrostatic latent image is performed by detecting voltage variation generated between the first electrode layer and the second electrode layer owing to the electric discharge, as current variation with a current detection amplifier or the like.
Now, in the above-described radiation image recording medium, if a method such as vacuum deposition is used as a method for providing the first electrode layer on a surface of the recording photoconductive layer, such deposition of an electrode material takes place in a state that the radiation image recording medium is supported via a peripheral portion of the recording photoconductive Layer while the surface of the recording photoconductive layer is facing downward. Accordingly, an area of the first electrode layer to be provided becomes smaller than an area of the recording photoconductive layer by an area equivalent to an area of the peripheral portion. Even if the first electrode layer is provided by use of other fabricating methods, it is still difficult to form the first electrode layer exactly in the same area as the recording photoconductive layer. As a result, a small area without provision of the first electrode layer is incurred on the peripheral portion of the upper surface of the recording photoconductive layer. Meanwhile, if the first electrode layer is provided in the exactly same area as the recording photoconductive layer, then electric discharge against the second electrode layer tends to increase. Therefore, there may be a case that provision of the first electrode layer in a smaller area than the recording photoconductive layer as described above is rather preferred.
However, if the size of the first electrode layer is smaller than the size of the recording photoconductive layer as described above, corona discharge occurs at an end portion of the first electrode layer when a direct-current voltage is applied between the first electrode layer and the second electrode layer upon recording a radiation image. As a result, negative electric charges generated by this discharge are charged on a surface of the peripheral portion of the recording photoconductive layer where the first electrode layer is not provided. The negative electric charges leaking out of the end portion of the first electrode layer are injected into the recording photoconductive layer. Furthermore, the injected negative electric charges are accumulated in the electric accumulator after passing through the recording photoconductive layer. Thereafter, the negative electric charges charged on the surface of the peripheral portion owing to the above-described corona discharge and the negative electric charges accumulated in the electric accumulator owing to injection of the electric charges collectively form electric field distribution between the second electrode layer and the negative charges themselves. Such an electric field distribution will not be deleted but retained even after short-circuiting the first electrode layer and the second electrode layer upon the above-described retrieval. In other words, a virtual image is recorded with respect to the above-described peripheral portion even where the image is not supposed to be recorded originally.
Meanwhile, in the above-mentioned radiation image retrieving apparatus, an electromagnetic wave for retrieval is irradiated linearly in a main scanning direction with a line light source, for example, and then irradiated two-dimensionally over the entire surface of the second electrode layer by scanning in a sub-scanning direction. Alternatively, a beam electromagnetic wave is irradiated by scanning in the main scanning direction and the sub-scanning direction, whereby the electromagnetic wave is irradiated two-dimensionally over the entire surface of the second electrode layer. Therefore, when the electromagnetic wave for retrieval is irradiated onto the entire surface of the second electrode layer as described above, the electromagnetic wave for retrieval is also irradiated onto a region of the second electrode layer corresponding to the above-described peripheral portion (a non-imaging portion). Accordingly, charge pairs which are generated in the retrieving photoconductive layer are discharged attributable to the electric field distribution, and such discharge generates a large false image signal. Since such a false image signal is intense, the false image signal affects an image signal to be retrieved from an imaging region, thus causing deterioration of image quality. Moreover, since a false image signal attributable to the negative electric charges charged on the surface of the peripheral portion by the corona discharge has a particularly intense time constant, such a false image signal greatly affects the image signal to be retrieved from the imaging region. In addition, it is impossible to remove the false image signals mixed in the image signal upon retrieval from the imaging region as described above by subsequent image processing or the like.
In consideration of the foregoing problem, an object of the present invention is to provide an image recording medium, an image retrieving method and an image retrieving apparatus capable of enhancing image quality of an image without generating the false image signal as described above even in the case where the size of the first electrode layer of the image recording medium is smaller than the size of the recording photoconductive layer as described above.
An image recording medium according to the present invention concerns an image recording medium including a first electrode layer which transmits an electromagnetic wave for recording, a recording photoconductive layer which takes on conductivity by receiving irradiation of the electromagnetic wave for recording, an electric accumulator which accumulates electric charges for a latent image generated on the recording photoconductive layer, a retrieving photoconductive layer which takes on conductivity by receiving irradiation of an electromagnetic wave for retrieval, and a second electrode layer which transmits the electromagnetic wave for retrieval, the image recording medium being formed by stacking the foregoing constituents in accordance with the above order of enumeration. Here, the image recording medium is characterized in that a size of the first electrode layer is smaller than the recording photoconductive layer and the recording photoconductive layer thereby includes a peripheral portion on an upper surface thereof on which the first electrode layer is not provided, and a light-shielding film is provided for shielding irradiation of the electromagnetic wave for retrieval onto a non-imaging region of the retrieving photoconductive layer corresponding to the peripheral portion.
Here, the foregoing aspect that the xe2x80x9csize of the first electrode layer is smaller than the recording photoconductive layerxe2x80x9d refers to an aspect that the size of the first electrode layer is smaller than the recording photoconductive layer from a viewpoint of a stacking direction (a direction indicated by an arrow S in FIG. 1) of the respective layers of the image recording medium.
Moreover, the foregoing xe2x80x9cnon-imaging region of the retrieving photoconductive layer corresponding to the peripheral portionxe2x80x9d refers to a region of the retrieving photoconductive layer in the same range as the peripheral portion from the viewpoint of the stacking direction of the image recording medium.
Furthermore, the foregoing xe2x80x9cshielding irradiation of the electromagnetic wave for retrieval onto a non-imaging regionxe2x80x9d refers to an action of shielding the non-imaging region from irradiation of the electromagnetic wave for retrieval either entirely or partially.
Furthermore, the foregoing xe2x80x9clight-shielding filmxe2x80x9d may be provided anywhere so far as the light-shielding film can shield the non-imaging region of the retrieving photoconductive layer from irradiation of the electromagnetic wave for retrieval. For example, the light-shielding film may be disposed on a face of the retrieving photoconductive layer corresponding to the non-imaging region where the electromagnetic wave for retrieval is irradiated, a surface of the second electrode layer corresponding to the non-imaging region, a surface of a predetermined support corresponding to the non-imaging region if the image recording medium is disposed on the support, or the like.
Furthermore, the image recording medium can be designed in a manner that the electromagnetic wave for retrieval is irradiated onto the second electrode layer two-dimensionally by scanning in a main scanning direction and in a sub-scanning direction, and the light-shielding film can be designed to shield at least one of the end regions, which are located at both end portions of the non-imaging portion in the sub-scanning direction, from irradiation of the electromagnetic wave for retrieval.
Here, if the electromagnetic wave for retrieval is irradiated from a line light source onto the image recording medium, for example, then the foregoing xe2x80x9cmain scanning directionxe2x80x9d refers to a longitudinal direction of the line light source, and a direction approximately orthogonal to the longitudinal direction is referred to as the xe2x80x9csub-scanning directionxe2x80x9d. Meanwhile, if the electromagnetic wave for retrieval is irradiated onto the image recording medium by scanning with beam light, then the foregoing xe2x80x9cmain scanning directionxe2x80x9d refers to a direction in which the beam light is linearly irradiated and a direction approximately orthogonal to the direction of such linear irradiation is referred to as the xe2x80x9csub-scanning directionxe2x80x9d.
Moreover, the light-shielding film can be also designed to shield irradiation of the electromagnetic wave for retrieval onto an edge portion of an imaging region adjacent to the non-imaging region shielded from irradiation of the electromagnetic wave for retrieval.
Here, the foregoing xe2x80x9cimaging regionxe2x80x9d refers to a range of the retrieving photoconductive layer in the same range as the first electrode layer from a view point of the stacking direction of the image recording medium.
Moreover, it is preferable that the foregoing xe2x80x9cend portion of the imaging regionxe2x80x9d is a region within the imaging region where the image therein is less important or a region which is a margin of the image.
An image retrieving method according to the present invention concerns an image retrieving method using an image recording medium, which includes a first electrode layer which transmits an electromagnetic wave for recording, a recording photoconductive layer which takes on conductivity by receiving irradiation of the electromagnetic wave for recording, an electric accumulator which accumulates electric charges for a latent image generated on the recording photoconductive layer, a retrieving photoconductive layer which takes on conductivity by receiving irradiation of an electromagnetic wave for retrieval, and a second electrode layer which transmits the electromagnetic wave for retrieval, the image recording medium being formed by stacking the foregoing constituents in accordance with the above order of enumeration. The image retrieving method performs retrieval by irradiating the electromagnetic wave for retrieval two-dimensionally by scanning in a main scanning direction and in a sub-scanning direction with respect to the second electrode layer of the image recording medium in which the electric charges for a latent image are accumulated into the electric accumulator thereof by irradiation of the electromagnetic wave for recording, and by obtaining an electric signal at a level corresponding to a quantity of the electric charges for a latent image which are accumulated in the electric accumulator by the irradiation. Here, the image retrieving method is characterized in that a size of the first electrode layer of the image recording medium is smaller than the recording photoconductive layer thereof and the recording photoconductive layer thereby includes a peripheral portion on an upper surface thereof on which the first electrode layer is not provided, and the electromagnetic wave for retrieval is not irradiated onto a non-imaging region of the second electrode layer corresponding to the peripheral portion.
Here, the foregoing xe2x80x9cnon-imaging region of the second electrode layer corresponding to the peripheral portionxe2x80x9d refers to a region of the second electrode layer in the same range as the peripheral portion from a viewpoint of a stacking direction of the image recording medium.
Moreover, as for the foregoing method in which xe2x80x9cthe electromagnetic wave for retrieval is not irradiatedxe2x80x9d, for example, a power source of a light source or the like, which generates the electromagnetic wave for retrieval, may be turned off not to generate the electromagnetic wave for retrieval. Alternatively, the electromagnetic wave for retrieval may be shielded by a predetermined light-shielding member or the like. Moreover, the method may be carried out in a manner not to irradiate the entirety of the non-imaging region or not to irradiate a part of the non-imaging region.
Moreover, the method can be designed not to irradiate the electromagnetic wave for retrieval onto at least one of the end regions located at both end portions of the non-imaging portion in the sub-scanning direction.
Furthermore, the method can be also designed not to irradiate the electromagnetic wave for retrieval onto an edge portion of an imaging region adjacent to the non-imaging region on which the electromagnetic wave for retrieval is not irradiated.
An image retrieving apparatus according to the present invention concerns an image retrieving apparatus which includes: an image recording medium including a first electrode layer which transmits an electromagnetic wave for recording, a recording photoconductive layer which takes on conductivity by receiving irradiation of the electromagnetic wave for recording, an electric accumulator which accumulates electric charges for a latent image generated on the recording photoconductive layer, a retrieving photoconductive layer which takes on conductivity by receiving irradiation of an electromagnetic wave for retrieval, and a second electrode layer which transmits the electromagnetic wave for retrieval, the image recording medium being formed by stacking the foregoing constituents in accordance with the above order of enumeration; retrieving light irradiating means for irradiating an electromagnetic wave for retrieval two-dimensionally by scanning in a main scanning direction and in a sub-scanning direction with respect to the second electrode layer of the image recording medium in which the electric charges for a latent image are accumulated in the electronic accumulator thereof by irradiation of the electromagnetic wave for recording; and image signal obtaining means for obtaining an electric signal at a level corresponding to a quantity of the electric charges for a latent image which are accumulated in the electric accumulator owing to irradiation of the electromagnetic wave for retrieval by the retrieving light irradiating means. Here, the image retrieving apparatus is characterized in that a size of the first electrode layer of the image recording medium is smaller than the recording photoconductive layer thereof and the recording photoconductive layer thereby includes a peripheral portion on an upper surface thereof on which the first electrode layer is not provided, and the retrieving light irradiating means does not irradiate the electromagnetic wave for retrieval onto a non-imaging region of the second electrode layer corresponding to the peripheral portion.
Moreover, the retrieving light irradiating means can be designed to include a light-shielding member for shielding the electromagnetic wave for retrieval, and the electromagnetic wave for retrieval is not irradiated onto the non-imaging region by use of the light-shielding member.
Moreover, the retrieving light irradiating means can be designed not to irradiate the electromagnetic wave for retrieval onto at least one of the end regions located at both end portions of the non-imaging portion in the sub-scanning direction.
Furthermore, the retrieving light irradiating means can be designed to include a light-shielding member for shielding the electromagnetic waver for retrieval, and the retrieving light irradiating means can be designed not to irradiate the electromagnetic wave for retrieval onto at least one of end regions located at both end portions of the non-imaging portion in the sub-scanning direction by use of the light-shielding member.
Furthermore, the retrieving light irradiating means can be also designed not to irradiate the electromagnetic wave for retrieval onto an edge portion of an imaging region adjacent to the non-imaging region on which the electromagnetic wave for retrieval is not irradiated.
Furthermore, the retrieving light irradiating means can be also designed not to irradiate the electromagnetic wave for retrieval onto an edge portion of an imaging region adjacent to the non-imaging region on which the electromagnetic wave for retrieval is not irradiated by use of a light-shielding member.
In addition, the image recording medium may further include other layers in addition to the above-described layers.
According to the image recording medium, the image retrieving method and the image retrieving apparatus of the present invention, the electromagnetic wave for retrieval is not irradiated onto the non-imaging region of the retrieving photoconductive layer corresponding to the peripheral portion where the first electrode layer is not provided on the upper surface of the recording photoconductive layer. Therefore, it is possible to avoid retrieval of a false image signal, which is attributable to corona discharge at an end portion of the first electrode layer and injection of electric charges from the end portion of the first electrode layer into the recording photoconductive layer, whereby a deterioration of an S/N ratio of the image signal under an adverse influence of the false image signal can be prevented and image quality can be thereby enhanced.
Moreover, if the electromagnetic wave for retrieval is arranged not to be irradiated onto at least one of the end regions located at both end portions of the non-imaging region in the sub-scanning direction, then it is possible to avoid retrieval of a false image signal corresponding to the end region of the non-imaging region immediately before scanning the imaging region when the false image signal is particularly apt to affect the image signal. Accordingly, it is possible to attempt further enhancement in image quality.
Moreover, if the electromagnetic wave for retrieval is also arranged not to be irradiated onto the edge region of the imaging region adjacent to the non-imaging region on which the electromagnetic wave for retrieval is not irradiated, then it is possible to avoid the adverse influence by the false image signal more sufficiently.
Furthermore, according to the image recording medium of the present invention, the electromagnetic wave for retrieval is shielded by the light-shielding film. Therefore, the above-mentioned effects are obtainable with a simple constitution.
Furthermore, according to the image retrieving apparatus of the present invention, if the electromagnetic wave for retrieval is arranged not to be irradiated by use of a predetermined light-shielding member, then the above-mentioned effects are obtainable with a simple constitution of the apparatus.